This invention relates to electron spectrometers, in particular for the surface analysis of a sample.
Hitherto, electron spectrometers in surface analysis instrumentation have been of two main types. The first type namely the hemispherical analyzer (HSA), has been employed primarily in X-ray photoelectron spectroscopy (XPS), where the primary irradiation, namely X-rays, was used to bombard and release electrons from a relatively large area of sample, typically 0.1-1 square centimeter, and it was necessary to provide means to collect the released electrons from this relatively large area and deliver the collected electrons to the analyzer. For this purpose an electron lens system has generally been employed, in a position between the sample under examination and the analyzer, in a mode which essentially could be described as one of collimating electrons ejected from the whole irradiated area and focusing these to a point which was at the entrance of the analyzer.
The second type, namely the cylindrical mirror analyzer (CMA), has hitherto been employed in Auger electron spectroscopy (AES) particularly in applications where the source of irradiation, namely electrons, was focused on to small areas of the sample of the order of 1 square micron or even less. In this application the geometrical arrangement of the electron gun used as the source of the primary irradiation enabled electrons ejected from the small irradiated area to be collected over a large solid angle, typically 0.5 steradians, and thus maximise sensitivity in this mode of operation.
The HSA could be used for high spatial resolution AES but hitherto had the disadvantage of low sensitivity, because the input lenses to the HSA were, as described above, essentially collimators and useful only to collect electrons over small angles, for example less than 5.degree. half-angle.
Similarly the CMA could be used for XPS applications, but again the geometry was such that it was impossible to obtain maximum resolution in this mode whilst maintaining the high collection efficiency of the system required for high spatial resolution AES.
In previous practice, electron spectrometers have been used as described for example in British Patent Specification No. 1,332,207 comprising a hemispherical analyzer, means for irradiating a sample located in a sample position to cause electrons to be emitted therefrom, an electron optical lens system which includes a plurality of elements for receiving the electrons emitted from the sample and delivering the received electrons to the analyzer, a detector connected to the analyzer to detect analyzed electrons and energized means for applying potentials to the elements such that electrons which are ejected from a restricted selected area of the sample are brought to a focus by the lens system.